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At least 109 records · Page 6Linked to original sources
PubMed1975

Regulation of thyroid ornithine ornithine decarboxylase (ODC) by thyrotropin. I. The rat.

We studied the effects of TSH on rat thyroid ornithine decarboxylase (ODC) activity. After 1 day of goitrogen treatment, there was an abrupt fall in serum triiodothyronine (T3) a rise in circulating TSH, and a dramatic increase in thyroid ODC activity. Despite the continued rise in TSH and progressive increase in thyroid gland size with further treatment, thyroid ODC activity declined on the third day and remained at submaximal levels. Thyroid ODC activity was also stimulated in a dose-related manner by administration of exogenous TSH. Little TSH effect was noted before 3 h. Maximal ODC activity occurred between 4 and 5 h. The TSH stimulation of ODC could be inhibited by pretreatment with actinomycin D or cycloheximide, suggesting that the increase in ODC activity requires new RNA and protein synthesis. Although pretreatment with agents that alter microtubule structure (e.g., colchicine and vinblastine) prevent stimulation of ODC activity by TSH, additional data suggest, but do not confirm, that hrmone secretion and ODC activation may be dissociable. Further studies were undertaken to determine whether cyclic AMP (cAMP) or prostaglandins played any role in the regulation of thyroidal ODC activity. Dibutyryl cAMP, alone, or together with aminophylline, did not stimulate thyroidal ODC activity in dosages which concomitantly stimulated adrenal enzyme activity. Likewise, prostaglandin E2 (PGE2) did not stimulate thyroidal ODC activity, but did stimulate adrenal enzyme activity in a dose-related manner. However, pre-treatment of rats with inhibitors of prostaglandin synthesis prevented the activation of thyroidal ODC BY TSH. One inhibitor, indomethacin, attenuated the TSH stimulation of enzyme activity in a dose-related manner. Indomethacin pretreatment also resulted in approximately a 10-fold decrease in thyroidal prostaglandin levels. Exogenous PGE9, in dosages as high as 500 pg, did not overcome the inhibitory effect of indomethacin on ODC activation. Although the precise role for endogenous prostaglandins remains to be defined, it does appear that a reduction in thyroidal prostaglandins prevents activation of the enzyme by TSH.

Animals↗
PubMed1990

Expression of human chromosome 2 ornithine decarboxylase gene in ornithine decarboxylase-deficient Chinese hamster ovary cells.

Ornithine decarboxylase (ODC) belongs to a multigene family and some of these may very well be nonfunctional (pseudogenes). We isolated an ODC gene from a human chromosome 2-specific library and transfected the gene into ODC-deficient Chinese hamster ovary cells to directly demonstrate that this ODC gene is functional and ODC is essential for cell proliferation. After screening 2.5 X 10(5) plaques using a human ODC complementary DNA probe, a typical clone with a 5.4-kilobase insert was isolated and then cloned into the HindIII site of the pGem-1 vector. One (phODC 2B1) of these clones containing a 5.4-kilobase ODC gene insert was identified. Restriction enzyme analysis and partial sequencing data revealed that phODC 2B1 contained the full length protein-coding sequences but lacked first exon and 3'-polyadenylation sequences. Primer extension analysis indicated that human ODC mRNA has homologous sequences with the ODC gene from human chromosome 2. To determine that the chromosome 2 ODC gene is functional, ODC-deficient Chinese hamster ovary cells were transfected with the ODC expression vector (phSV2B1-neo) and several G418-resistant transfectants were isolated which expressed 70- to 400-fold more ODC activity than parental or wild-type Chinese hamster ovary cells. Furthermore, these stable transfectants exhibited a higher growth rate than wild-type cells. These results indicate that the ODC gene from human chromosome 2 encodes functional ODC protein, and ODC (and its product putrescine) is required for cell growth.

Animals↗
PubMed1990

Influence of the 5'-untranslated region of ornithine decarboxylase mRNA and spermidine on ornithine decarboxylase synthesis.

The effect of the 5'-untranslated region of ornithine decarboxylase (ODC) mRNA and of spermidine on the translation of ODC mRNA was studied in a rabbit reticulocyte cell-free system. The ODC mRNAs, possessing different sizes of the 5'-untranslated region and named mODC241, mODC188, mODC85, and mODC24 according to the number of nucleotides in the 5'-untranslated region, were synthesized by in vitro transcription techniques through the use of plasmids containing various sizes of mouse ODC cDNA. As the size of the 5'-untranslated region of ODC mRNA increased, the efficiency of the translation decreased and the degree of stimulation of the translation by 0.2 mM spermidine increased. The inhibition of ODC mRNA translation by high concentrations of spermidine (0.6-1 mM) also increased with an increase in the size of the 5'-untranslated region. The spermidine effects were increased greatly when the size of the 5'-untranslated region of ODC mRNA was increased from 85 to 188 nucleotides. These results suggest that the nucleotides 70-220 upstream from the initiator AUG are involved in the decrease in translational efficiency. In addition, at least the nucleotides in the 70-170 region upstream from the initiator AUG are important in the strong stimulation of ODC synthesis by low spermidine concentrations and in the inhibition of ODC synthesis at high spermidine concentrations.

Animals↗
PubMed1985

Ontogeny of food deprivation effects on ornithine decarboxylase: ornithine decarboxylase induction by alpha and beta agonists.

Short-term food deprivation (FD) of preweanling rat pups causes a marked and specific suppression of liver ornithine decarboxylase (ODC) induction by alpha and beta adrenergic agonists that is mediated by postreceptor mechanisms. In the present study, we demonstrate that FD also affects the ability of adrenergic agonists to induce hepatic ODC in older animals and that these changes differ from those occurring in neonates in the duration of FD associated with changes, the subcellular mechanisms involved and the organ specificity of the effect. FD (48 hr) of 30-day-old rats caused a specific suppression of liver ODC induction by the alpha agonist phenylephrine whereas the effect of the beta agonist isoproterenol was not changed. ODC induction by vasopressin or angiotensin was unaffected, whereas the effect of aminophylline was potentiated. FD of 30-day-old rats caused a marked suppression of both alpha and beta agonist action in the heart. FD of mature (60-day-old) rats was associated with an enhanced hepatic ODC response to phenylephrine and isoproterenol. Whereas the number of receptors in heart assessed by the binding of [3H]prazosin and [125I]pindolol to alpha and beta receptors, respectively, decreased in parallel with changes in responsivity, liver ODC responses did not correlate well with receptor changes. These findings support previous findings of altered sympathetic responsivity in heart, liver and fat during FD and indicate that the sympathetic nervous system responds to FD with a complex series of changes in both pre- and postsynaptic mechanisms.

Adrenergic alpha-Agonists↗
PubMed1988

Regulation of ornithine decarboxylase mRNA translation by polyamines. Studies using a cell-free system and a cell line with an amplified ornithine decarboxylase gene.

The translational control of ornithine decarboxylase (ODCase) by polyamines has been studied using a cellular as well as a cell-free system. A mutant L1210 cell line, in which ODCase represents 4-5% of all soluble protein synthesized, was isolated by stepwise selection for resistance to the ODCase inhibitor 2-difluoromethylornithine (DFMO). The exceptionally high expression of ODCase in these cells was due to amplification of the ODCase gene. When the cells were grown in the absence of DFMO, dramatic increases in cellular putrescine and spermidine levels occurred. These increases were accompanied by a rapid decrease in ODCase synthesis. The change in ODCase synthesis was not associated with an alteration in the amount of ODCase mRNA, demonstrating a translational control in these cells. The effects of polyamines on ODCase mRNA translation were also studied in rabbit reticulocyte lysates using mRNA isolated from the DFMO-resistant cells. Low concentrations of spermidine stimulated synthesis of ODCase and that of total protein, when added to gel-filtered lysates. Notably, optimal stimulation of ODCase synthesis was achieved at a spermidine concentration lower than that required for an optimal rate of total protein synthesis. Higher concentrations of spermidine were inhibitory, and their effects of ODCase synthesis were stronger than on protein synthesis in general, resulting in a decrease in the fraction of protein synthesis accounted for by ODCase. The present results demonstrate that at least part of the feedback regulation of ODCase exerted by the polyamines is due to direct inhibition of ODCase mRNA translation.

Animals↗
PubMed1997

Brucella abortus arginase and ornithine cyclodeaminase genes are similar to Ti plasmid arginase and ornithine cyclodeaminase.

Brucella abortus arginase and ornithine cyclodeaminase genes have been cloned and sequenced. These gene sequences are located in the same operon and occur in the same order as the homologous genes in Agrobacterium tumefaciens Ti C58 plasmid. The nucleotide sequences of the two genes have 72% and 65% identity to the respective Ti plasmid genes. Both genes are present in a single copy, and expression of arginase is regulated in response to arginine.

Agrobacterium tumefaciens↗